Recorders of this general type usually comprise a housing having a swing-out door hinged to the housing. A stylus or pen driven by a galvanometer or torque motor is mounted in the housing with the stylus engaging a bearing surface on the housing. The door can be opened to permit a roll of paper to be inserted into the housing. The paper is drawn from the roll and trained around the bearing surface under the pen and thence leads out of the housing by way of driven rollers. The rollers are driven at a constant rate, while at the same time the torque motor responds to the signal to be recorded and drives the pen back and forth over the paper thereby imprinting a data trace on the paper. The recorder disclosed in U.S. Pat. No. 4,253,104 is typical of prior apparatus of this general type.
In order for the trace to be accurate, it is essential that the paper movement through the recorder be smooth and uniform. To accomplish that objective, conventional recorders have tended to be unduly complex and costly, employing expensive high-torque drive motors with integrated gear trains and numerous bushings and bearings on the moving parts of the recorder. The drive motors commonly used for this purpose are not only expensive, but also they are relatively noisy so that, when a large number of such recorders are operated in a confined space, they present a noise problem.
The prior recorders typified by the one in the aforesaid patent are disadvantaged also in that when loading a new roll of paper into the recorder, the recorder itself must advance the chart paper along the flow path through the recorder. This requires the operator to insert the paper roll into the recorder, feed the leading edge of the paper strip through the recorder until that edge touches the drive rollers and then turn on the recorder's drive mechanism so that the drive rollers engage the strip and advance the leading end out of the recorder. Since in some applications the paper roll must be replaced relatively often, the total reloading downtime involved can be considerable.
Other disadvantages of prior conventional strip chart recorders include the rewinding of the exiting end of the paper strip into the recorder, the inability to tear the exiting paper strip in both upward and downward directions and a relatively complicated pen lift and carriage locking mechanism.